Azeotropic cleaning solvents based on 1 1 2 2-tetrachloro-1 2-difluoroethane

ABSTRACT

THE DISCLOSURE RELATED TO BINARY AND TERNARY AZEOTROPIC MIXTURES OF TETRACHLORODIFLUOROETHANE. THE BINARY AZEOTROPES CONTAIN TETRACHLORODIFLUOROETHANE AS ONE COMPONENT AND EITHER ACETIC ACID, PROPIONIC ACID, DIOXANE, MONOMETHYL ETHER OF ETHYLENE GLYCOL, ETHYL ACETATE, ISOPROPYL ACETATE OR N-PROPLY ACETATE AS THE SECOND COMPONENTS. THE TERNARY AZEOTROPES CONTAIN TETRACHLORODIFLUOROETHANE AS THE FIRST COMPONENT, 1,2-DICHLOROETHANE AS THE SECOND COMPONENT AND EITHER METHANOL, ETHANOL OR ISOPROPANOL AS THE THIRD COMPONENT. IT HAS BEEN DISCOVERED THAT THESE AZEOTROPES MAY BE USED IN SOLVENT VAPOR CLEANING AND DEGREASING APPLICATIONS.

United States Patent 1 i 3,640,884 AZEOTROPIC.CLEANING= SOLVENTS BASED 0N 1,1,2,Z-TETRACHLORO-1,2-DIFLUOROETHANE. John Allan Schofield, Irvington, and Roger A. Delano,

Dobbs Ferry, N.Y., assignors to Union Carbide Corporation, New York, N. Y. A No Drawing. Filed Oct. 28, 1968, Ser. No. 771,334 Int. Cl. C09d 9/00; C11d 7/52; C23g /02 US. Cl. 252-171 2 Claims ,ABSTRACT OF THE DISCLOSURE The disclosure relates to binary and ternary azeotropic mixtures of tetrachlorodifluoroethane. The binary azeotropes contain tetrachlorodifiuoroethane as one component and either acetic acid, propionic acid, dioxane, monomethyl ether of ethylene glycol, ethyl acetate, isopropyl acetate or n-propyl acetate as the second components. The ternary azeotropes contain tetrachlorodifluoroethane as the first component, 1,2-dichloroethane as the second component and either methanol, ethanol or isopropanol as the third component. It has been discovered that these azeotropes may be used in solvent vapor cleaning and degreasing applications.

This invention relates to binary and ternary azeotropic mixtures of tetrachlorodifluoroethane. The binary azeotropes contain tetrachlorodifiuoroethane as one component and either acetic acid, propionic acid, dioxane, monomethyl ether of ethylene glycol, ethyl acetate, isopropyl acetate or n-propyl acetate as the second component. The ternary azeotropes contain tetrachlorodifluoroethane as the first component, 1,2dichloroethane as the second component and either methanol, ethanol or isopropanol as the third component. It has been discovered that these azeotropes may be used in solvent vapor cleaning and degreasing applications.

Chlorofluoroethane solvents known in the art ordinarily do not have sufiicient solvent power to clean printed circuit boards; that is, to effectively remove the rosin flux and other contaminants deposited on the surface of such boards during the application of conductive metal leads thereto. Ultrasonic or vapor degreasing techniques may be used to improve the cleaning action of such solvents. Although mixtures of solvents have been used for this purpose they have the disadvantage that they boil over a range of temperatures and consequently undergo fractionation invapor degreasing or ultrasonic applications which are open to the atmosphere. Additionally, when employing either of these methods the solvent must also" the vapor has more of a tendency to dissolve high melting greases, or fluxes as'well as oil residues and the like and at a faster rate. When articles such as circuit boards are 3,640,884 Patented Feb. 8, 1972 thear't'icle passing through the degreaser up to-the vapor temperature of the solvent, Consequently higher boiling solvents generally allow for longer periods of cleaning action per unit of time in a continuous vapor degreaser than the lower boiling solvents. g

Tetrachlorodifluoroethane also is a better solvent tor most types of materials than trichlorotrifluoroethane however, it suffers the disadvantage that it is solidus at room temperature whereas the latter is liquidus. Accordingly tetrachlorodifluoroethane is more difiicult to handle than liquid type cleaning solvents.

It is an object of this invention to provide a constant boiling or azeotropic solvent that is a liquid at room temperature, will not fractionate and also has the foregoing advantages. Another object is to provide an azeotropic composition which is valuable as a solvent for oils and greases and particularly for cleaning printed circuits. A further object is to provide an azeotropic composition which is both relatively nontoxic and nonfiammable both in the liquid phase and in the vapor phase and which at the same time is an excellent solvent for cleaning printed circuits especially by continuous vapor degreasing or ultrasonic means.

The above object of this invention may be accomplished by novel mixtures comprising a two component composition of tetrachlorodifluoroethane (e.g. l,1,2,2-tetrachloro- 1,2-difluoroethane) as a first component and either acetic acid, propionic acid, dioxane, monomethyl ether of ethylene glycol, ethyl acetate, isopropyl acetate or n-propyl acetate as a second component. The above objects of this invention may also be accomplished by novel mixtures comprising a three component composition of tetrachlorodifluoroethane (e.g. 1,1,2,2-tetrachloro-1,2-difluoroethane) as a first component, 1,2-dichloroethane as a second component and either methanol, ethanol or isopropanol as a third component.

Although 1,1,2,2-tetrachloro-1,2-difluoroethane is a preferred tetrachlorodifluoroethane component, the isomer 1,1,1,2-tetrachloro-2,Z-difluoroethane may be substituted as a component therefore in whole or in part and especially in minor amounts or trace amounts. All of these aforementioned mixtures form azeotropes which distill at a constant temperature, the liquid phase and the vapor phase in equilibrium therewith having the same composition. Such mixtures are relatively nontoxic in both the liquid phase and the vapor phase.. These mixtures are particularly useful as solvents for greases, oils, waxes and the like and are particularly useful for cleaning printed circuits.

Although the aforementioned azeotropic mixtures are obtained at approximately 760 mm. Hg a variation in pressure and consequently a change in the compositions and boiling points are also intended to be within the broad scope of the invention. Thus the azeotropes may contain many different proportions of the aforementioned components provided a constant boiling mixture is obv tained at the various pressures at which the compositions passed through aivapor degreaser, the solvent 'vaporstend to condense on the article until the articles are heated by the vapors'from room temperature to the temperature of the vapor. The condensation thus formed on the articles tends to drip back into the solvent reservoir taking with it some of the soil on the article. For this reason the ability of a cleaning solvent to condense on and wet the 8 surface is especially advantageous. Higher boiling solvents prolong this condensation effect in a continuous degreaser since it takes a greater amount of time. to bring are used. Stated otherwise any pressure may be employed to obtain the azeotropes of this invention as long as a two component or three component constant boiling mixture is obtained, and accordingly the ratio of components of the azeotropes of theinvention will also vary. The variation of components is thus within the skill of the art and is easily determined once it is known that the organic compounds of this invention will form the aforementioned azeotropes. In a preferred embodiment the present invention relates to the aforementioned azeotropes that boil at atmospheric pressure 1- about 25, especially i about 15 mm. Hg pressure.

-. -An azeotropic composition is obtained by distilling a mixture, of -1,1-, 2,2 tetrachloro-l,2 difiuoroethane and acetic acid. The mixture is charged to a laboratory scale A printed circuit board coated with a rosin flux is cleaned in'an ultrasonic degreasing apparatus with the azeotropic mixtures of this invention and substantially all of the rosin flux is removed Without any observable distillation flask having an overhead condenser with pro f g ffi f ll board whlch constitutes the backvision for the removal of the distillate. The mixture g pnnfe U f is heated to its atmospheric boiling point and distilled 6 fi 10.11 0 f g 0 t 15 mven g i at-ahighreflux. An azeotropic mixture is obtained cong g q e gi n e .2 a z con sisting essentially of about 93.0 parts 1,1,2,2-tetrachloro- 0 mm e o owl an emary sys ems of tetrachlorodifiuoroethane listed in Table II' 1,2-d fiuoroethane and about 7.0 parts acetic acid on a weight basis, based on refractive index analysis, the boil- TABLE II ing point of which is about 194.3 F. measured at substantially 760 m1ll1meters Hg pressure. Systems Which Did Not Form Azeotmpfis EXAMPLES 2-10 Components The process of example one is repeated using the com- (1 Binary ponents noted in Table I and the composition is meas- 1,1,2,2-tetrachloro-1,Z-difiuoroethane/acetone ured by gas chromatographic analysis and the boiling 1,1,2,2-tetrach1oro-1,Z-difiuoroethane/benzene pomts of each z r pe 18 mea r s in Table I- 1,1,2,2-tetrachl0ro-1,Z-difluoroethane/chloroform TABLE I 1,1,2,2-tetrachloro-1,2-difiuoroethane/cyclohexane 1,1,2,2-tetrachloro-1,2-difiuoroethane/ 1,1-dich1oro- Normal ethane 09mm. 3,1 5 1,1,2,2-tetrachlorol,2-diiluoroethane/heptane N Components Sltion 1 F.) 2 2 5 1,1,2,2-tetrachloro-1,2-d1fiuoroethane/ methylene Binary azetropes chloride 1 NMLZtHZ-tetiICachIOro-I,Zdifiuoroethane 93.0 194. 3 lletzfiiientachloro-l2{hfluorOethane/Perchloroce 0 ac 7.0 2 --{111ymtetmehhmlizdifluomethane' )95 199-3 1 1 2 2-tetrachloro-1 Z-difiuoroethane/toluene Propionie acid 5 3 {1,1,2,2-tetrachloro-1,Zfiifiuoroethane. 88.0 197.3 1,lll-tetfachloro-LZ-dIHUOIOBthaHE/ Dioxane 12.0 4 i1,1,2,2-tetrachloro-l,2jdiflu0roethane 91.8 197 mchloroethane Mogo rethygletherlogfitgyleneglycol. 8.3 2 1 (2) Ternary 5 1,1,, erac oro 1 uoroe one.. 7. 17.

{Ethyl acetate 92's 1,1,2,2 tetrachloro 1,2 difluoroethane/methanoll 6 {%,1,2,2-tet1rachgo0-1,2-difluoroethane. 192.0 water 7 7 ,fggfgfgg1ggggg, 9A 1910 1,1,2,2-tetrachloro-1,2-d1fiuoroethane/perchlorop acetate 6 ethylene/ methanol Ternary azetropes 1, 1,2,2-tetrachloro-1,Z-difiuoroethane/perchloro- 1,1,2,2-tetrachloro-l,Z-difluoroethane 55.0 ethylene/ethanol s {11v,I2-$chl01roethane 133.3 1,1,2,2-tetrachloro-1,2-difluoroethane/perchloro- 8 am) 1,1,2,2tetraehl0ro-1,2-d1fluoroetl1ane. 44. 0 ethylene/lsopropanol 9 {1,2 dichloroethane 33.0 158. 5

Ethanol 23.0 1,1,2,2-tetrachloro-1,?rdifiuoroethane 37.0 Because of the fluctuation in ambient pressures as dis- 10 hgg gggggf 3%}; 165-4 cussed previously, the compositions of the azeotrope cornlPercent y weight ponents as well as their equivalents noted herein will also 2 -760 mm. Hg pres sure. vary as fOllOWs.

TABLE III Component Composition, parts by weight Binary azeotlopes Acetic acid About 93 partszlzabout 10%, especiallyiabout 5%; about 7 1 partsiabout 10%, especiallydzabout 5%. Propionie acid About partsiabout 10%, especlallydzabout 5%; about 5 Dioxane AiifiifififiiiiQfifi? iti i iiii zabo t 57 b t 12 y u a on partszhabout 10%, especia l lyiabont 5%. 0 Monomethyl other of ethylene glycol About 91.8 partszlzabout 10%, espeeiallyiabout 5%; about 8.2

partsiabout 10%, espeeiallyzizabout 5%. Ethyl acetate About 7.2 partsztzabout 10%. especiallydzabout 5%; about 92.8

partszhabout 10%, especiallyiabout 5%. Isopropyl acetate About 23.7 parts-iabout 10%, especlallyiabout 5%; about 76.3

partszlzabout 10%, especiallyiabout 5%. n-Propyl acetate About 9.4 partsiabout 10%, especiallyzlzabout 5%; about 90.6

1,1,2,2-tetrachloro-l,2-difluoroethane partsiabout 10%, especlallydzabout 5%.

Ternary azeotropes 1,2-diehloroethane Methanol 1,2-diehloroethane Ethanol 1,2-dichloroethane Isopropanol.

partszbabout 10%, especiallyzlzabout 5%; about 28.0 partsd: about 10%, especiallyzizabout 5%. }About 44 partszbabout 10%, especlallyiabout 5%; about 83 }About 55.0 partsiabout 10%, especlallyiabout 5%; about 17.0

partszlzabout 10%, espeelallyiabout 5%; about 23 parted: about 10%, especiailydzabout 5%.

About 37 partsiabout 10%, espeelallydzabout 5%; about 38 partszbabout 10%, especiallyiabout 5%; about 25 partsd:

about 10%, espeeiallyzhabout 5%.

In the following claims it is intended that the components contained therein as well as those of Table III herein and their disclosed and art known equivalents, be construed in such a manner so that for example 1, 1,2,2- tetrachloro-l,2-difluoroethane in an amount of about 93 parts 2: about 10% shall mean about 83.7 parts to about 102.3 parts on a weight basis and likewise for the other components noted in Table III and the claims as well as their equivalents, especially those equivalents noted herein.

Although the invention has been described by reference to some preferred embodiments it is not intended that the broad scope of the novel azeotropic compositions be limited thereby but that certain modifications are intended to be included within the spirit and broad scope of the following claims.

What is claimed is:

1. A composition of matter consisting essentially of an azeotrope which at about 760 millimeters of mercury pressure and at about 165 F. consists essentially of about 37 percent by weight 1,1,2,2 tetrachloro 1,2-difluoroethane, about 38 percent by weight 1,2-dichloroethane and about 25 percent by weight of isopropanol.

References Cited FOREIGN PATENTS 9/1968 Germany.

OTHER REFERENCES Mellon, Industrial Solvents, Reinhold Publ. (1950), p. 75.

LEON D. ROSDOL, Primary Examiner W. E. SCHULZ, Assistant Examiner US. Cl. X.R. 

